docs: def _print_MatMul(self, expr):
          """
          Matrix multiplication printer. The sympy one turns everything into a
          dot product without type-checking.
          """
          from sympy import MatrixExpr
          links = []
          for i, j in zip(expr.args[1:], expr.args[:-1]):
              if isinstance(i, MatrixExpr) and isinstance(j, MatrixExpr):
                  links.append(').dot(')
              else:
                  links.append('*')
          printouts = [self._print(i) for i in expr.args]
          result = [printouts[0]]
          for link, printout in zip(links, printouts[1:]):
              result.extend([link, printout])
          return '({0})'.format(''.join(result))